Blowing in the wind: Millions wasted on wind farms without a breeze

For anyone building a wind farm, it might seem an unnecessary piece of advice - put it somewhere windy.

Astonishingly, however, many turbines are going up on sites which are simply not breezy enough, energy consultants have claimed.

They say farms are being built in the "wrong places" because of the pressure to hit Government targets in the race to produce green energy.

But the "badly sited and underperforming" turbines are not reliable enough to keep the nation's television sets, toasters and lights switched on.

Michael Jefferson, an independent engineering consultant and former economist for Shell, said the industry often exaggerated the amount of energy each farm would supply.

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New sites are assessed on the basis of average wind speeds over a year - a measure called the "load factor".

The industry recommends an average load factor of 30 per cent for a turbine to operate efficiently.

Yet although the load factor can be as high as 45 per cent in parts of Scotland and Wales, some farms achieve less than 20 per cent, he said.

Only five wind farms in the east of England achieve load factors of 30 per cent or more: "That's just five out of 25," he said.

"We should be putting our money where the wind is and that is quite often not where the development pressure is.

"Even in a high average-wind-speed area you really have to be absolutely precise as to where you site them.

"In Cumbria, for instance, you've got two - one which achieves a load factor of about 36 per cent and the other a mere 2.3km away which achieves just 20 to 21 per cent."

The Government wants 15 per cent of Britain's electricity to be generated by wind farms and other renewable energy sources by 2014.

Jim Oswald, an engineering consultant, said wind speeds were too unreliable and variable to meet that target. "It's the power swings that worry us," he said. "Over a 20-hour period you can go from almost 100 per cent wind output to 20 per cent.

"When you have a very large number of wind farms on the grid and that happens, you are talking about massive power swings on the system."

To cope with the variation in wind energy over a normal day, gas and coal generators would need to be turned on and off continually.

"They are not designed for that, and the net effect is to put them under mechanical strain and also increase their carbon dioxide," said Mr Oswald.

However, the wind farm industry dismissed the claims, which were raised in BBC Radio 4's Costing The Earth programme. Market forces ensured wind turbines had to be placed in windy areas, it said.

The Government no longer subsidises new wind farms. Instead, it sets targets for power suppliers, forcing them to sell a fixed proportion of green electricity each year, or pay a penalty under the Renewable Obligations Certificates scheme.

The British Wind Energy Association's chief executive Maria McCaffery said the scheme rewarded wind energy companies for each unit of electricity produced - and not for building wind farms.

"Wind speeds vary across the country, which is why most wind farms are concentrated in key areas," she said.

"No one in their right mind would build turbines where they wouldn't produce a viable amount of electricity."

Most farms generate electricity 85 per cent of the time, she added. Not every wind farm can be built on sites with the most wind because of technical problems and planning objections.

There are 1,876 wind turbines in Britain, generating 2,191 megawatts of electricity - enough to power 1.2million homes.